The proposed project develops a system to improve construction safety by emphasizing the engineering aspects, and further incorporates other aspects pertinent to the engineering control system (e.g., procedural, behavioral, social, and economic aspects). The proposer will develop SAFETY FIRST, a fault tree expert system for investigating and avoiding construction slips and falls from the same and higher elevation structural members used during construction. It is expected that the system could be used to minimize construction accidents and improve construction safety. Specifically, the research focuses on the following: 1. To provide the user a tool with which to investigate a construction accident that has already occurred. 2. To provide the user with a consulting tool that will explain the contributing causes of potential accidents. At the final stage of the research, SAFETY FIRST models will be tested for their validity by the knowledge engineer, participating experts, and other experts using real construction accidents. In order to achieve the specific aims of our proposed project, we will combine two innovative research methods, namely, the fault tree system and expert system. Fault tree models are employed to represent the knowledge obtained from experts and from literature concerning the causal relationships among events/causes leading to a construction accident. The expert system simulates the way experts determine the accident causes , so that engineers may employ the pooled knowledge to the best advantage.